1. Field of the Invention
This invention relates to laying heads of the type employed in high speed rod mills to form the hot rolled exiting product into a helical formation of rings.
2. Description of the Prior Art
A conventional laying head is schematically depicted at 10 in FIG. 1. The laying head includes a housing 12 containing a hollow quill 14 rotatably supported between front and rear roller bearing assemblies 16 and 18. The quill 14 carries a bevel gear 20 meshing with a mating bevel gear 22, the latter being driven in a conventional manner by a gear box and motor (not shown).
A laying pipe 24 is carried by the quill 14. The laying pipe has an entry end 24a aligned with the rotational axis X of the quill, and a curved intermediate section 24b leading to an exit end 24c spaced radially from the axis X.
In a typical modern day high speed rolling operation, a finished rod with a 5.5 mm diameter exits the mill a speeds on the order of 112-120 m/sec and at a temperature in the range of 750 to 1100° C. The rod can either be delivered to the laying head at these elevated temperatures, or it can be water cooled down to about 600-950° C. before it enters the entry end 24a of the laying pipe. The curvature of the laying pipe, coupled with its rotation about axis X, forms the rod into a helical series of rings R. The rings are delivered to a cooling conveyor (not shown), on which they are distributed in an offset overlapping pattern for additional cooling prior to being gathered into coils.
When operating under these conditions, the laying head can attain rotational speeds on the order of 1500-2250 RPM and higher, and the rotating components of the laying head, including the roller bearing assemblies supporting the quill, can be exposed to temperatures a high as 100-110° C. The roller bearing assemblies must thus be designed with adequate clearances to accommodate thermal expansion and contraction.
It has now been determined that, particularly in the front bearing assembly 16, which is relatively lightly loaded, at certain speeds such clearances can cause detrimental roller skidding and vibration.